The simulator is continuing to execute instructions beyond the end of your code. Add a SIMHALT instruction to halt the simulator.
Code:
*-----------------------------------------------------------
* Title :
* Written by :
* Date :
* Description:
*-----------------------------------------------------------
ORG $1000
START: ; first instruction of program
MOVE.B #14,D0 ; Display string task
LEA EM,A1 ; Location of string
TRAP #15 ; Execute task
MOVE.B #3,D0 ; Display number in D1 task
MOVE.B N1,D1 ; Get number in N1
ADD.B N2,D1 ; D1 = D1 + N2
TRAP #15 ; Execute task
; halt simulator
SIMHALT
N1 DC.B 4
N2 DC.B 5
EM DC.W 'The Number Added ',0
END START ; last line of source